Telephone system



Feb. 18, 1941.

' R. TAYLOR arm.

TELEPHONE SYSTEM Filed April 2, 1957 9 Sheets-Sheet 1 INVENTORS REGINALD TAYLOR- ee Tnoms BAKER Am Feb. 18, 1941. T O ETAL 2,232,189

TELEPHONE SYSTEM Filed April 2, 1937 9 Sheets-Sheet 2 F192. YA

/N VENTOPS REGINALD TAYLOR ijflQGE THOMAS BAKER ATTY Feb. 18, 1941. TAYLOR r 2,232,189

TELEPHONE SYSTEM Filed April 2, 1957 9 Sheet-Sheet s I 4 6. v QWISJER 5 IN VEN TOR 5 REGINALD TAYLOR ATTY Feb. 18, 1941. R TAYLOR r 2,232,189

TELEPHONE SYSTEM Filed April 2, 1937 9 Sheets-Sheet 4 I F 4b V METER-F a) KDI 11 7W Rims: "02

INVENTORS IPU z ZM M I REGINALD TAYLOR Z GEORGE moms BAKER 7 Z Z ATTY Feb. 18, 194-1. TAYLOR ETAL 2,232,189

TELEPHONE SYSTEM 7 Filed April 2, 1937 9 Sheets-Sheet 5 M2 43 M4 SC lAlVENTOPS REGINALD TAYLOR GEORGE THOMAS BAKER Feb. 18, 1941. R. TAYLOR EI'AL.

TELEPHONE SYSTEM Filed April 2, 1937 9 Sheets-Sheet 6 INVENTORS REGINALD TAYLOR GEORGE THOMAS BAKER Feb. 18, 1941.

R. TAYLOR El AL TELEPHONE SYSTEM Filed April 2, 1937 DIM DAQ Dn3\) 9 Sheets-Sheet 7 H an 7 IN VE N TOPS REGINALD TAYLOR GEORGE THOMA5 BA HEP ATTX Feb. 18, 1941. R. TAYLOR ETAL 2,232,189

TELEPHONE SYSTEM Filed April 2, 1937 9 Sheets-Sheet 8 6D M2 M3 4 50 a 0A F03 LcoZ cof ca6 Yo? 4014 A I 3 2:: g M 8 m5 D SD 1 1 2 5 650 IN VENTORS REGINALD HYL 0!? TTY Feb.'18, 1941. R. TAYLOR ETAL 2,232,189

TELEPHONE SYSTEM Filed A ril 2, 1937 9 Sheets-Sheet 9 INVENTORS REGINALD TAYLOR GEORGE THOMAS BAKER Patented Feb. 18, 1941 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Application April 2, 1937, Serial No. 134,500 In Great Britain April 3,1936

10 Claims.

The present invention relates to telephone systems and is more particularly concerned with systems having a plurality of interconnected exchanges such as for instance a main exchange associated with a number of satellite exchanges.

With such systems it is usual to employ at the satellite exchange an automatic switch which discriminates between local and outgoing calls and sets up a local call after absorption of 1 one or more digits while possibly serving only as an impulse repeater for outgoing calls. Such a switch is known as a discriminating selector repeater.

It is the main object of the present invention to provide improved arrangements for route discrimination, digit absorption, zone metering and barred access control and which are so constructed that one portion may be capable of functioning without alteration in othersystems for instance in a system employing register controllers. The improved arrangements can be simply adapted for use in satellite exchange networks of varying complexity and thus produce substantial economies in manufacture and generally simplify the work of exchange maintenance.

According to one feature of the invention the discriminating portion and the selector portion of the arrangement are formed as independent units, and the selector portion is made capable of functioning either as a first code selector for use in a register controller system incorporating zone metering or in a multi-exchange system such as for example a satellite exchange system with zone metering and route discrimination under control of a separate discriminating unit accessible in common to a plurality of selector portions. Preferably also the zone metering equipment of this unit is distinct from the route discrimination equipment so that the two functions may be determined after different numbers of digits have been received.

The invention will be better understood from the following description of one method of carrying it into effect, reference being had to the accompanying drawings comprising Figs. 1 to 9 which should be arranged as shown in Fig. which is inserted at the right hand corner of Fig.3.

Figs. 1, 2 and 3 show the circuits of a selector and an associated hunter switch which are intended to function in two capacities. On the one hand they may be employed as a first code selector and an A digit selector hunter in a register controller system with provision for zone metering facilities which may be either level controlled or controlled from the register controller. On the other hand the selector and hunter may be used in a manner to be described in conjunction with the sending unit and discriminating unit shown in Figs. 4, 5 and 6, and '7, 8 and 9 respectively to form a discriminating arrangement with control of metering from the discriminating unit. In the latter case the outgoing junctions to the main exchange are connected to the first level of the selector, this level being reserved for this purpose; no separate junction hunter switch is therefore required.

Figs. 4, 5 and 6 show the circuits of a sending unit which is accessible. from the selector of Figs. 1, 2 and 3 over the hunter switch and includes a mechanical impulse regenerating device of the type disclosed in J. W. McClew and C. R. Woodlands application No. 79,830, filed th May 1936, which is adapted to receive and store trains of impulses. Upon receipt of a signal from the discriminating unit, the received impulse trains are sent out in regenerated form to actuate either the satellite or parent exchange selectors in accordance with the route discrimination determined in the discriminating unit. Facilities are also provided to absorb certain digits in response to signals from the discriminator by arranging to short-circuit the pulsingout leads until such time as these unwanted digits have been sent out by the impulse regenerator.

Figs. 7, 8 and 9 show the circuits of a discriminating unit which is directly associated, with the sending unit and comprises essentially a 3 uniselector which is set by the calling subscribers dialled impulses in parallel with the impulse regenerator. The uniselector bank contacts are marked between successive impulse trains and according to the particular cross-connection employed it is possible in response to the dialling of one or more routing digits to effect the determination of the appropriate meter fee and of the proper route for the call.

The two-directional switch employed in the selector is assumed to be of the type disclosed in R. N. Saxbys Patent No. 2,028,639, granted 21st January 1936, having a so-called rectangular motion while the unidirectional switches employed are of the well-known reverse drive type.

For the purpose of the description any connections which are alterable to suit the conditions to be met are inserted in chain dotted form, the connections referred to being those from the CO and DA terminals in the discriminating unit to the CO and DA terminals in the sending unit and also those from the banks of the D switch to various terminals in the discriminating unit.

Considering first the operation of the equipment on a call' from a regular subscriber it will be assumed, that his line is extended to the selector shown in Figs. 1 to 3 by way of a line finder or other non-numerical switch. Immediately the selector is seized relay L operates over the incoming line loop in series with the iron hydrogen current limiting device BRA and at armature ll operates relay A and I in series to earth over resistance YA, (relay D being nonoperative in this condition due to rectifier MRE being in a conductive direction) and at armature 12 operates relay B. A circuit is thereby closed for the lower winding of relay C over armature bI and a2, while relay BB operates over armature b2. Relay BB in operating thereupon at armature bbl applies guarding potential to the incoming P conductor while relay C in operating at armature c3 completes a self-- interrupted driving circuit for the sending unit hunter switch magnet SUHM from earth which is connected to a common lead II by way of equipment which is arranged to give a delayed alarm in case of failure to release, armatures k2 and m4, wiper H in the home position, armatures c3 and M3, interrupter contacts suhm, magnet SUHM to battery.

Accordingly the switch rotates in search of a disengaged'sending unit which is marked by battery potential on the associated P contact. When the test wiper P encounters a tree outlet relay K operates quickly overt-earth, resistance YD, armatures al and m2, windings of relay Kin series, P wiper and P lead to battery over armatures 006 and resistance YE in parallel with the left-hand winding of relay IA in the idle sending unit. Relay K upon operating at armature k2 disconnects the magnet driving circuit to arrest the motion of the switch and at armature kl extends a guarding and holding potential by way of its low resistance lower winding; at the same time the short circuit is removed from relay KR which now operates from earth over resistance YD, winding of relay KR, contacts m3, c5, resistance YB to battery. The upper winding of relay K is energised in an opposing direction to its lower win-ding in order to enable it to release in the case of a dual connection. In the case of a dual connection the two K relays are arranged to operate from the same idle marking battery but the holding flux produced in each, due to the current through their low resistance lower windings will be halved while the opposing flux due to their upper windings will remain the same. In these circumstances both the K relays will re lease and cause the hunter switches to continue searching. Due to the difference in the speed of any two switches, after a few steps one will reach a free outlet before the other, whereupon the associated K relay will operate to guard the outlet and disconnect the driving circuit. This testing arrangement enables relay K to difierentiate accurately between the hold and release currents under single and dual connections respectively.

Relay KR upon operating, at armatures kr3, kr4, kr5, krfi and kr'l switches the control leads through to the sending unit, whereupon earth is extended from armatures Z2 and krl over the PU lead to hold re'lay IA in the sending unit, this relay having been initially operated over its lefthand winding in series with relay K. A loop by way of armatures Im2 and id in the sending unit is returned over the negative and positive conductors to maintain relay A operated in the selector. Relay IA in operating at armature I (ll operates relay IB in series with the impulse regenerator receiving magnet MR, the resistance YG serving to prevent false impulses to the magnet MR when all three springs of relay IA are in contact. Relay IB in operating at armature IbI completes a locking circuit for itself, at ar-.

mature Ib3 lights the supervisory lamp ILP from earth which is connected to common lead 20 by way of delayed alarm equipment, at armature Ibl connects relay TI? to the S pulse cam for a purpose to be described later, while at armature Ib5 earth is connected to the common holding lead HL whereupon relay LR is operated. Relay LR in operating at armature 1T2 connects an earthed dial tone transformer over common lead 2| and condenser QB on to the FR lead extending to the selector when the dial tone finds a circuit through condenser QA and the earthed upper winding of relay I, whereupon it is applied to the incoming speaking conductors in a balanced circuit by induction through the windings of this relay. At armature lrl the left-hand winding of relay IA is disconnected from the incoming P-lead but this relay remains held over the earthed pulselead PU on its right-hand winding.

It will be noticed that the idle marking battery connected to the P lead initially comprises the left-hand winding of relay IA and resistance YE in parallel and on operation of relay LR consists.-

- quent holding or releasing condition for the selector K relay.

The subscriber now dials the first digit and relay L in the selector responds and at armature 12 repeats the impulses over the PU lead to relay IA in the sending unit. Each time relay IA releases a circuit is completed to energise the impulse regenerator receiving magnet MR as follows:-earth, armatures IbI, Ial and e05, magnet MR to battery while at the same time relay IC is energised in parallel. On each release of relay IA a circuit is also completed to energise the magnet DM of the switch in the discriminating unit as follows:earth, key contacts K132, armatures I b5 and Ia2, IPU lead, armature zm2, magnet DM to battery. Accordingly the digit is mechanically stored in the impulse regenerator in a manner to be described, while the switch D in the discriminating unit is advanced to a position corresponding to the digit dialled. During the impulse train it will be noticed that relay IB is intermittently short-circuited by the resting armature Ial but this relay will remain held due to the slugging effect of the short-circuited winding, while relay IC will hold during the impulse train due to its slug. It will be readily understood that neither the magnet MR nor relay IC will either operate or hold in series with relay B and moreover the inductance of the relay IB is such that it has no appreciable effect on the magnet performance.

It should be explained that the mechanical impulse generator hereafter termed regenerator comprises essentially a receiving ratchet wheel X which is rotated step-by-step under control of the receiving magnet MR and which is arranged on one side of a fixed disc Z carrying round its periphery a row of 40 pins. The rotation of the receiving disc stores up energy in a clock spring to drive the sending disc Y and thus actuate the impulse springs IMP and send out regenerated impulses of the correct character and rate. Before the reception of the first digit, the armature of a so-called marking magnet is resting on a pin in the disc Z which it has pushed forward to restrain the sending disc Y. During the first digit relay lC operates and holds during the impulse train and at armature I03 energises the marking magnet MM which tilts a lever carried by the receiving disc X out of engagement with the pins. At the end of the digit the receiving disc will have been rotated a number of steps equal to the number of impulses in the train and on release of relay lC the marking magnet is de-energised and allows the lever carried bythe receiving disc X to tilt back towards the disc Z thereby displacing a corresponding pin into the path of the disc Y thus virtually storing the digit dialled. Hence if the successive digits dialled are 5, 4 and 7 pins numbers 5, 9 and 16 from the original resting positions are displaced. It should be noted that the sending disc Y is at present restrained by the pin which was displaced at the end of the previous call. When the receiving disc is first moved oif normal, the off normal springs MN close and at the end of the digit when relay lC releases relay ON operates over contacts MNI and armature lcl and locks to the operated off normal contacts at armature onl and at armature on2 disconnects the dial tone.

Meanwhile the D switch in the discriminating unit Figs. '7, 8 and 9 has also been stepped by the trains of impulses and in a manner to be de scribed more fully later determines whether the call is to be routed locally or by way of an outgoing junction to the parent exchange, this discrimination taking place after the first, second, or third digit.

Assuming first that the call is to be routed through the'parent exchange, then after reception of one, two or three digits earth will be applied to the JD lead extending from the discriminating unit to the sending unit whereupon relay JD will be operated over its right-hand winding and at armature adl locks to the earthed holding lead HL. Relay JD in operating at armaturea'dz operates relay LD and at armature 7'd3 operates relay IP whilst at armature :id4 it opens the hold-- ing loop for relay A in the selector over the outgoing negativeand positive conductors. Relay LD in operating at armature ldl disconnects relay LR and hence during the release time of this relay the outgoing loop to relay A in the selector will be opened, but on release, armature 11-3 again extends a loop by way of the impulse springs IMP and armature lm2 to re-operate relay A.

Referring now to the selectorcircuit, relay A in releasing at armature a2 completes a circuit from earth by way of armatures bl, a2 and cl to energise the vertical magnet VM in series with the low resistance upper winding of relay C and accordingly the selector wipers are raised to the first level on which are wired the outgoing junctions to the main exchange whereupon the on normal contacts N are mechanically operated and at contacts NI extend earth from armature 02 to operate relays HB and HA over their middle windings. On re-operation of relay A, the vertical magnet energising circuit is disconnected while relay C now releases after a short interval due to its slug since its preenergising circuit over its lower winding is disconnected at ofi normal contacts N2. Relay C in releasing at armature c2 completes an energising circuit for the rotary magnet RM from earth, armatures bb3, ml, dbl, hb3, ha3, rotary magnet interrupter contacts rm, ofi normal contacts Nl, armature c2, magnet RM to battery and the wipers will therefore be advanced into engagement with the first set of the contacts in the level selected whereupon the rotary all normal springs NR will be mechanically operated while the magnet interrupter contacts rm will also be opened.

If both the outlets encountered by the PI and P2 wipers are engaged, that is, they are marked by the presence of earth potential on the test contact, relays HB and HA will be maintained operated on their right-hand windings and the disconnection by the contacts rm of their initial operating circuits over their middle windings is therefore Without effect. However the rotary magnet RM which is connected in parallel with these relays releases and when the interrupter contacts again close the magnet is again energised to advance the wipers on to the nextset of contacts. This stepping operation continues automatically until either a free outgoing junction to the main exchange is found or alternatively the wipers are advanced to the 11th position.

Assuming now that the wiper P2 is the first to encounter a free outlet, there will be no earth potential to hold relay HA operated when the interrupter contacts rm open and this relay will quickly restore and atarmature ha3 open the driving circuit while the selected outlet is immediately guarded from earth, armatures had and hb l and the P2 wiper. Relay HB will however remain held from the busy marking potential picked up by wiper Pl. A circuit is now completed from earth, armature bl, rotary oif normal contacts NR2 and armature ha to operate relay BA and thereupon at armatures ba2, ba4, ha I, hb-l and hb5 the negative and positive pulsing out leads from the sending unit are switched through to the lower set of negative and positive wipers whereupon the loop extended from the sending unit now operates the A and B relays in the main exchange incoming switch in preparation for the reception of regenerated pulses. Armature bal disconnects the right-hand winding of relay HB from the testing wiper Pl and this relay now holds as follows: earth, armatures bb3, ml, dbl, hb3 and M13 to battery over its left hand winding.

If however the Pl wiper is the first to encounter a free outlet, relay HB releases to open the magnet driving circuit at armature hb3 while the outlet selected is immediately guarded over this wiper from earth, armatures hbG, D126 and m8. Relay BA will be operated as previously described and extends the loop from the sending unit over the upper set of wipers through to the junction.

In case both test wipers encounter free outlets, both test relays HA and HB 'restore whereupon relay BA is energised as above and relay HA is re-operated on its left-hand winding from earth, armatures bb3, ml, dbl and hb3 and rotary oil normal contacts NRI. The pulsing out loop is therefore switched through to the upper set of wipers and it will be seen that priority is always given to the upper set of wipers in these circumstances.

If all the outlets in the level selected prove busy the wipers are rotated to the '11th position where the cam springs S are mechanically oper ated. Relays HA and HB release since the PI and P2 wipers encounter no earth potential and relay BA is thus energized. Relay HA is then reoperated as before and switches the pulsing out loop to the upper set of negative and positive wipers and since they are resting on unwired contacts the stored pulses subsequently transmitted from the sending unit will be sent out into an open circuit and thus do no harm. Cam contacts S2 connect the upper winding of relay I in circuit with the busy tone transformer which is connected to common conductor 16 whereupon busy tone is returned to the subscriber in a balanced circuit to inform him that he must hang up and re-dial.

Returning now to the sending unit, relay LR on releasing at armature lr completes a circuit to operate relay P from earth, regenerator oil normal contacts MNI, fixed disc Z which is in contact with a pin left projecting from a previous call, the reset pin in the disc Y which bears against the former pin, sending magnet interrupter contacts ms, armature lr5, winding of relay P to battery. Relay P in operating at armature p2 energizes the control switch magnet CNM, at armature p3 disconnects relay IP, at armature p4 prepares an energizing circuit for the regenerator sending magnet MS, and at armature p5 completes a locking circuit for itself. The release time of relay IP is arranged to be of the order of 600 milli-seconds which period allows the selector ample time to hunt for a free outlet and on release of this relay the regenerator sending magnet MS is energised whereupon relay P now releases since its holding circuit is disconnected at both the interrupter contacts cnm and ms, associated with the magnets CNM and MS respectively. Relay P in releasing re-operates relay IP at armature 123 in preparation for provlding the next interdigital pause while at armatures p2 and p4 the magnets CNM and MS are de-energised whereupon the CN wipers are advanced to position 2. During the operation of the sending magnet MS the reset pin is moved to restore to its normal position the movable pin in the disc Z against which it has been resting and the sending disc Y is now free and rotates due to the wound clock-spring and operates the impulse springs IMP to send out impulses over the outgoing negative and positive leads, the first train of pulses sent out serving to set the main exchange selector. The sending disc rotates until it encounters the pin displaced at the end of the first dialled digit when relay P will be energised as before and will again open the circuit of relay IP and the sending out of the second digit will be held up until relay IP fully releases. This process is repeated for each digit stored and it will be appreciated that the regenerator is capable of receiving and transmitting impulse trains simultaneously. It will be seen that for this type of call the dialled digits are merely regenerated and retransmitted.

The necessary multi-fee registration is set up in accordance with the digits dialled from the discriminating unit over the metering leads M2, M3 and M4 on to relays IMA and IMB and is retransmitted to the selector. For example if relay IMB only is operated, relay MB in the selector will be operated on its right-hand winding in series with the magnet SUHM over the MB lead and connects up to the double fee metering lead at armature mb3 whilst if relay l MA only is operated relay MA in the selector will be oper- I ated in a circuit over earth, resistance YF (Fig. 6), armature lma4, FR lead, FR bank and wiper, armature lcr5, upper winding of relay MA in series with the right-hand winding of relay M to battery, the YF resistance being such that relay M cannot operate in this circuit: relay MA in operating at armature ma2 connects up the triple fee metering lead. I! both relays MA and MB are operated the quadruple metering lead will be connected up, whilst if neither is operated the single fee lead is connected up.

After all switches in the train have been set the wanted subscriber, if free, will be signalled in a normal manner by ringing current transmitted from the final selector in the train and when he answers, the current will be reversed over the speaking conductors so that rectifier MRE bridged across relay D in the selector will no longer be in a conductive direction thus allowing this relay to operate. 'I'hereupon at armature dl it connects up the left-hand winding of relay DA to the S pulse cam of the meter delay set and at armature d2 prepares a locking circuit for this relay over its middle winding. The delay set comprises so-called S and Z pulse cams arranged to supply battery pulses with a definite time relation to two corresponding leads. On transmission of the next S pulse, relay DA will be operated and at armature da5 prepares a circuit for relay DB which is operated after the appropriate time interval from the Z pulse in series with the righthand winding of relay DA. Relay DA remains locked over its middle winding in series with resistance YC until relay DB operates on the Z pulse when both the initial energising circuit and the locking circuit for relay DA are opened but this relay remains held on its right-hand winding in series with the lower winding of relay DB for the duration of the Z pulse. During the application of the Z pulse relay RG is connected by way of armatures d412, dal and the armatures of relays MA and MB to the selected metering lead and in accordance with the setting of these two latter relays, relay RG will be operated a predetermined number of times and at armature rgl will repeat these pulses over the incoming P conductor in the form of booster battery pulses to actuate the subscriber's meter. At the end of the Z pulse, relay DA restores to prevent any further operation of the metering relay RG while relay DB remains operated from earth via armatures bb3 and ml on its upper winding in series with the left-hand winding of either relay HA or relay HB since the upper winding is no longer short-circuited at armature dbl.

Assuming now that the call is to be routed over local switches the equipment is arrangedto absorb any unwanted digits. If, for example, it is arranged to absorb the first two digits, earth will be extended over the LD lead from the discriminating unit at the end of the third dialled digit, thus operating relay LD in the sending unit. This relay in operating at armature Zdl disconnects relay LR and also looks via this armature to the earthed holding lead. During the release time of relay LR no preliminary impulse is given to the A relay of the selector since relay JD is normal and maintains a loop across the outgoing negative and positive contacts by way of armatures HM and 7d4. On release of relay LR the regenerator is started up and sends out the two unwanted digits but these are nullified by the resting armatures Im2 and id across the impulse springs IMP while since relay IP is unoperated no interdigital pause is given between the absorbed digits. It will be remembered that the CN switch is stepped forward one contact before the sending out of each digit and thus during the sending of the first digit, wiperCN3 will be connected to tag DAI, during the second digit to tag DA3 and so on. During the sending out of the second unwanted digit wiper N3 will encounter earth on terminal DA3 which earth is extended from the discriminating unit in a manner to be later described and this earth energises relay IP. When relay P subsequently operates in a normal manner after the sending of this last absorbed digit, relay JD will be operated over its left-hand winding from-earth over armatures ipl and p6 and at armature :idl locks to the holding lead, at armature i113 disconnectsthe operating circuit of relay IP and at armature jdd removes the short circuit from across the regenerator impulse springs 1MP. On release of relay 1? thesending out is re-commenced and from this point it takes place in the manner described for a junction call except that the first selector is stepped to some level other than level one and therefore the main exchange equipment is not used. j 1

The general operation of the apparatus having been dealt with, the method of discrimination will now be described in more detail, reference being had to the discriminating unit. The meter and route discrimination arrangements provided are independent since it is possible that the junction discrimination might have to take place afterv the first digit whereas the appropriate meter fee might not be known until after the third digit and clearly meter discrimination cannot be effected until after the route has been determined.

In order to cater for complex numbering schemes it is necessary for route discrimination to take place after the first, second or third dialled digit and therefore if discrimination takes place after the second digit the first will have to be absorbed whilst if discrimination takes place after the third digit the first two digits will have to be absorbed. It will be assumed by way of example that an area has the following numbering scheme: routed to main exchange over level I (20006999, 8000-42999); routed to manual board over level 0 (0); routed to adjacent automatic exchange over level 3 (73000 to 73999); routed locally over levels -8 (71500-71899); routed locally over level 2 (72000-72599).

Consider first the case in which the main exchange number 8456 is dialled. In addition to the digit being stored on the regenerator in the manner previously described the first digit dialled will step the switch D to contact 9 (the home position being contact I) and at the end of this digit relay IC in the sending unit releases and at armature I02 extends the earthed holding lead over the C lead to wiper D'I. Since it is required to route the call through to the parent exchange, contact 9 on the D1 bank will be connected to ta m and thence by way of armature Ida-5 and a cross connection between tags it and a on to the JD lead. Thus relay JD in the sending unit will be operated at the end of the first digit and will cause the digit stored in the regenerator to be sent out in the manner hereinbefore described. The remaining digits in the number dialled further step the switch D for the purpose of determining the meter fee in the manner to be described later.

Assume now that the number 71822 is dialled, this being a local exchange number requiring the absorption of the first two digits 71. It will be remembered that on this type of call relay LD is operated from the discriminating unit at the end of the third dialled digit while it is necessary to earth terminal DAS in the sending unit. The terminals DA'I to DA3 in the sending unit are cross-connected to ter als DAI to DA! respectively in the discriminat ng unit to enable the necessary absorption to tgke place. In this example it will be necessary to operate relays IDA and IDB before operating relay LD in order to prevent the earth from the holding lead HL being extended on to terminals DAI and DA2. On reception of the first digit 7, wiper D1 will be stepped to contact I which is strapped to terminal J thereby operating relay IDA, which in operating at armature IdaI locks to the earthed lead HL while at armature Idal it disconnects the earth from the terminal DAI. The second digit 1 steps switch D further to contact 9 which is strapped to terminal m thereby operating relay IDB which locks and removes the earth from terminal DA2 at armature IdbS. On dialling the third digit 8 the switch is advanced to contact 17 which is strapped to terminal 9 whereupon earth will be extended at the end of this digit on to the LD lead byway of the cross-connection and armature ldb2. Relay LD in operating initiates the sending out of the regenerator as previously described for a local call. The following digits 22 further step the D switch in case the meter fee cannot be determined until the 4th or 5th digit.

It will be seen therefore on consideration that tags am and the associated contact combinations of relays lDA and IDB enable any num-, bering scheme to be catered for with discrimination on first, second or third digits. By the use of additional relays the discrimination may be deferred until the 4th and 5th digits, in which case terminals DA4 and DA5 in the sending unit would be brought into use. Since only one bank of the D switch, that is the D1 bank, is used to provide the route discrimination, it is necessary to provide the above arrangement to preclude any possibility of a call being incorrectly routed, where for example, the D switch is stepped to the same position in response to either main exchange or local or other routing digits. For example, on a junction call, digit 8 may be dialled as a first digit, at the end of which earth is extended over the D1 wiper in position 9 by way of tags m, k and a on to the JD lead whereupon relay JD will be operated; at the same time the dialling of the first two digits 71 of a local exchange number would also step the D switch to contact 9. In order to prevent the operation of relay JD in this case which would misroute the call, relay IDA is operated at the end of the first digit in the manner previously described, and at armature Idai thereupon changes over the link between contact 9 and the JD lead to relay IDB in preparation for the second digit 1.

The switch D is also used to determine theappropriatemeter fee and this may not be possible until as many as five routing digits have been dialled according to the complexity of the network. The D switch is further used for the important function of barring access to various routes under certain conditions. Assuming now that the dialling of two digits 73 will route the call into a particular meter fee zone, the switch D will he stepped to position 8 after the first digit and during the inter-digital pause earth will be extended 'over the C lead by way of resting armatures sd2, s02, sb! and sa! and thence via a strapping connection from contact 8 to terminal SA. Relay SA is thereupon operated and locks to the BL lead and at armature sai switches over the C lead on to the D2 wiper in preparation for the next digit. 0n reception of the next digit the switch is further stepped on to contact II while at the end of this digit earth will be extended by way of a strapping from contact II on the D2 bank to the appropriate meter fee terminal I-l or I (CCB barred), the use of the latter terminal being explained later. Should for example a double meter fee be required the connection will be taken from contact II on the D2 bank to terminal 2 and thence by way of armature r33 (relay RS being normally operated on a call from a regular subscriber) on to'the M2 lead and thence to the sending unit whereupon relay IMB is operated and this relay in turn operates relay MB in the first selector which connects up the double fee metering lead. Relay IMA or IMB in operating extends an earth over the ZM lead into the discriminating unit whereupon relay ZM is operated over its right-hand winding and at armature zm3 locks to the earthed holding lead HL. Armature zmI extends an earth by way of its left-hand low resistance winding to self-drive the D switch to the home position, since the remaining digits to be dialled need not actuate this switch. Furthermore on the subsequent release of the common equipment when all digits have been dialled it can be made more quickly available for further common use since there is no necessity to wait for the D switch to home. In the case of single fee calls relays IMA and IMB would not be operated, relay ZM being operated direct from the meter fee terminal I.

Relays SA to SD serve inefiect to increase the number of individual bank contacts over which the switch travels by switching the C lead as required and thus in conjunction with the banks D2-D6 the meter discrimination may be deferred until up to five digits have been dialled.

Relays CA, CB and CC provide cut-oil. conditions for varying numbering schemes in order that the common equipment can be released immediately a suflicient number of digits have been dialled. In the area assumed, for the five digit numbers, relays CA to CC will be unaffected and an earth would thus be extended over resting armatures ccB, chi; and ca6 on to terminal COI and thence via a cross connection to terminal 005 in the sending unit. Since the switch CN in the sending unit is advanced one step before each digit is sent out, wiper CN4 will be advanced to position 6 thereby making connection with terminal CO5 just prior to transmission of the 5th digit. At the end of this digit since there are no more digits stored in the regenerator the transmitting disc Y will catch up with the receiving disc X whereupon the ofi normal springs MN will be opened. There will thus be no circuit to operate relay P in the normal manner but relay ON will release and at armature 0118 it opens the holding circuit of relay IP. This relay releases after a short interval when relay COwill be operated from the earth encountered by the wiper CN4 and at armature 002 extends an earth on to the common conductor I8 extending to delayed alarm equipment which gives an alarm in case the apparatus fails to restore to normal causing it to release and at armature krl, krl to disconnect the control leads through to the sending unit and at armatures krfl and lcrI to connect the incoming speaking leads through to the negative and positive wipers. At armature krl a homing circuit is completed for sending unit hunter switch from earth on common lead I'I. Relay IA in the sending unit now releases and in turn releases relay IB which removes earth from the holding lead HL thus releasing all relays held thereunto whilst the switch CN is homed to one of its two home positions. Relay CO is maintained operated during the homing of this switch to guard the common equipment until all the apparatus therein has restored to normal.

For four digit numbers the meter discrimination is not wired direct from one of the banks D2 to D6 to the required unit tag but via a changeover contact of relay CA so that this relay operates before passing the signal to relays IMA, IMB or ZM. In this case therefore C0 tag 2 is wired to terminal 4 associated with the CN bank to give a cut-oil after four digits have been sent. Relays CB and CC are used for example to cater for single digit and six digit numbers respectively while if more than four different kinds of numbers exist in the same network additional relays are provided. Suflicient CO terminals are connected to the CNl bank to cater for a cut-01f after the sending out of up to nine digits.

On calls from regular subscribers, as soon as relay LR is operated in the sending unit, relay RS is operated on its right-hand winding over the RS lead, armatures 1T3, jdl and Im2, negative lead, winding of relay A in the selector to battery. On coin box calls however an earth is extended from the line finder over the D lead to the selector and serves to shunt relay RS and prevent its operation. It will therefore .be seen that the meter fee terminals I (CCB barred), 2, 3 and 4 are extended to the spare code lead SC thus operating relay IM at some point of the call.

1 This relay in operating, locks at armature ImI to the holding lead, disconnects the loop over the outgoing negative and positive conductors at armature Im2, prepares a circuit for earthing the forced release lead FR at armature Im3 and earthsthe ZM lead to home the D switch at armature Im4. The disconnection of the loop will prevent any further impulses sent out from the regenerator from being effective whilst if a junction call is being set up the distant equipment will be released. After all digits have been sent out from the regenerator relay ON will be released and on release of relay IP after its slow release period an earth will be extended on to the FR lead by way of armatures ipl, 011.4 and Im3. This delay period ensures a guarding overlap on junction calls, since on earthing the FR lead the junction is freed at the local outgoing end. Relay M in the selector is now operated on its right-hand winding and locks up over its lefthand winding at armature ml and also disconnects the holding circuit of relay DB and either relay HA or relay HB whichever is operated at the same armature, releases relay KR at armature m3, opens the homing circuit of the hunter switch SUH at armature m4, earths common lead I2 extending to supervisory equipment at armature m5, connects flicker earth over common lead I0 at armature m6 to the lamp LP which is connected to battery by way of delayed alarm equipment connected to common conductor I I so that in case relay M is maintained operated for longer than a predetermined period an alarm will be given while the lamp flashing will indicate the switch involved to the maintenance ofiicer. Armature m'l connects up the NU tone transformer over common lead l3 to the upper winding of relay I whence the tone is returned to the calling subscriber in a balanced circuit while armature m8 prevents an earth being extended on to the P lead when relay HB releases.

Either relay HA or H3 in releasing, frees either the junction or-the local train of switches while relay KR in releasing at armature krl removes the earth from the PU lead thus releasing relay IA and freeing the common equipment. During the release of this equipment relay CO will be operated and at armature e06 releases relay K in the selector which removes the guard earth from the P wiper at armature kl. Thus by taking the meter fee cross-connection in the discriminating unit to terminals I (CCB barred) 2, 3 and 4 coin box subscribers can be prevented from setting up certain single fee and all multifee calls without the intervention of an operator. Spare positions on the banks D2--D6 are also connected to the SC lead and hence if the subscriber dials a spare code he will receive NU tone.

Should the calling subscriber receive dial tone and then wait longer than a predetermined in the selector is then operated immediately over 1 the FR lead from earth by way of armatures ipl and 0M whereupon the common equipment is freed but no tone is returned to the subscriber since relay C has not yet been operated. Should the subscriber now dial relay A will respond in series with relays D and I when the selector will be raised vertically but cannot hunt in a rotary direction since the rotary magnet energising circuit is disconnected at armature ml. On release of relay C at the end of the first digit dialled the subscriber will receive NU tone in the normal manner whilst no more.impulses can be delivered to the vertical magnet since relay C cannot be re-operated.

If however the subscriber dials one or two digits and then'fails to dial the remainder, relay IM will be operated as above and in case the regenerator has not started-sending out due to the fact that the D switch in the discriminator has not received sufllcient digits to determine the type of call the FR lead will be earthed over resting armature M2 and armature I213.

The sending unit is provided with a so-called meter and time pulse disconnection key KD which allows a maintenance oflicer to efiect a continued routine on the unit without any operation of the tramc recorder and without the time pulse mechanism coming into efiect. A busying key KB is also provided which is operated when it is desired to busy-out the unit; on operation the supervisory lamp ILP is lit over 1 contacts KB3, the idle marking battery is disconnected from the incoming P conductor contacts KBl, the earth for the common lead is disconnected at contacts K32 and the operating earth for relay IB is disconnected at contacts KBI.

If any switch in either the sending or discriminating unit is moved ofl normal by hand for example, relay CO will be operated to guard the equipment during the homing of the switch.

On dialling the digit 0 the subscriber is routed to the manual board at the main exchange over a special set of junctions from the 0 level of the selector. cannot be completed on demand the operator may hold the connection by the application of battery to the positive lead and the subscriber may then restore his receiver. Relay L in the selector will then release but the battery connection will be extended over the positive lead, lower winding of relay I, armatures ll, do and d113, rectifiers MBA and MRB in a conductive direction and armatures dbl and ill to earth. Hence relay I is held operated and at armature il holds relay B and thus prevents release of the connection. Relay RG is non-operative in this condition as it is shunted by the rectifiers. When subsequently the operator desires to re-ring the calling subscriber in order to complete the call however, she operates her ring key which applies booster battery to the positive lead. This will find a circuit as before by way of the winding of relay I to earth but in this case rectifiers MBA and MRB will be non-conductive while rectifiers MR0 and MRD will become conductive and relay RG will therefore be operated. Armatures m2 and rail thereupon apply continuous ringing current over common leads l4 and i5 and armatures db6 and d'bl to the incoming speaking conductors and thus re-ring the calling subscriber. Armatures dbG and dbl serve to prevent ringing current being applied to the line when relay RG is being used as a meter pulse relay.

On any connection, when the calling party restores his receiver at the conclusion of conversation, relay L releases and opens the circuit of relay B. After a short period relay B releases and opens the circuit of relay BA which releases after a further short period. Armature ba3 thereupon removes earth from the incoming P conductor and also releases relay BB whereupon armature bbl reconnects earth to the P lead by way of the operated off normal contacts M3. Relay BB also at armature bb3 releases relay DB and either relay HA or relay HB, these relays being previously held in series. In case relay HA had been operated thus indicating that the upper set of wipers had been in use, the guard earth which was applied by way of armatures hbB, bbB and ml to the Pl wiper is now disconnected at armature bbB while in case relay MB had been operated to connect p the lower set of wipers, the guard earth normally applied by way of armatures ha and hbd to the P2 wiper will now be disconnected at armature hbl. It will be seen therefore that a double guard period represented by the sum of the release times of relays B andBA is provided on both the outgoing P leads in order to adequately cover the release of the distant exchange selectors and prevent the seizure of the junction before they have completely released. On release of relay BB a self-interrupted driving circuit is completed for the magnet RM from the earthed lead I1 and accordingly the wipers are rotated clear of the banks after which they fall and rotate under the banks under spring tension back to their normal positions where the off normal contacts NI open and disconnect the homing circuit. Preferably the rotary magnet is mechanically prevented from opening its interrupter contacts during the release movement so that there isv no tendency for it to chatter.

To facilitate testing, the test jack springs T are provided, their use being readily ascertained from the drawings. Furthermore each magnet is Should he require a trunk call which made from a portion of the received trains of impulses, means normally efiective during the regeneration of said trains of impulses to insert an interdigital pause between successive regenerated trains of impulses, and means controlling said last means to substantially prevent the insertion of an interdigital pause between successive trains of impulses which are regenerated but not re-transmitted.

2. In a telehpone or like system wherein connections are extended over automatic switches, a controller for operating said switches, means for seizing said controller and transmitting thereto a code of impulses to direct the extension of a connection, a first register in said controller operated by said impulses to register the whole of said code, a second register in said controller also operated by said impulses to register the whole of said code, means in said controller controlled by said first register for determining the path over which said connection is to be extended, means for operating the switches in accordance with said determination to extend the connection over said path, and means in said controller controlled by said second register independently of said first register and of the connection extended under control of said first register to assess an arbitrary value to said extended connection, said value depending upon part of the code registered by said second register.

3. In a telephone or like system wherein connections are extended over automatic switches, a register controller for operating said switches, means for seizing said register controller and for transmitting thereto a plurality of digits to direct the extension of a connection, means in said register controller for registering at least part of said digits transmitted to said register controller and for determining from said part thereof which of the digits transmitted to said register controller shall be retransmitted, other means in said register controller for registering all of said digits transmitted to said register controller and for retransmitting certain thereof in accordance with said determination made by said last means, thereby to operate said switches to extend said connection, and still other means in said register controller for registering at least part of said digits transmitted to said register controller and, in accordance with said part, assessing an arbitrary value to the connection extended by said switches under control of said retransmitted digits.

4. In a telephone or like system wherein connections are extended over automatic switches, a register controller for operating said switches, means for seizing said register controller and for transmitting thereto a plurality of trains of impulses to direct the extension of a connection, means in said register controller for receiving said trains of impulses and for subsequently retransmitting certain thereof to operate said switches to extend the connection, a discriminating switch in said register controller having a plurality of wipers operated by all of said received trains of impulses, a circuit completed over one wiper of said discriminating switch when a certain number of said trains of impulses have been received, means controlled over said circuit for determining which 01' the received trains of impulses shall be retransmitted and for controlling said last means to retransmit only those trains of impulses, another circuit completed over a different wiper of said discriminating switch when a certain number of said trains of impulses have been-received, and means controlled over said last circuit for assessing an arbitrary value to said connection extended by said automatic switches under control of said retransmitted trains of impulses, said value depending upon certain of the received trains of impulses.

5. In a telephone or like system wherein connections are extended over automatic switches, a register controller for operating said switches, means for seizing said register controller and for transmitting thereto a plurality of trains of impulses to direct the extension of a connection, means in said register controller for receiving and subsequently regenerating all of said trains of impulses, other means in said register controller for receiving said trains of impulses and for determining from certain thereof which, if any, of the regenerated trains of impulses shall be absorbed in said register controller, means for counting the regenerated trains of impulses, and means controlled conjointly by said last two means for at times preventing one or more of the regenerated trains of impulses from being transmitted to operate said switches.

6. In a telephone system or the like wherein connections are extended over automatic switches, control equipment, means for seizing said equipment and transmitting thereto trains of impulses each having a cretain digital value, means in said equipment responsive to said trains of impulses and effective subsequently to regenerate all thereof, separate means in said equipment also responsive to said trains of impulses and effective, upon said regeneration thereof, to at times suppress certain of the regenerated trains of impulses depending upon the digital values of one or more of the received trains of impulses, and means for transmitting only the unsuppressed regenerated trains of impulses to operate the automatic switches to extend a connection.

7. In a system as claimed in claim 6, means controlled by said separate means for at times initiating said regeneration responsive to the receipt of a certain number of trains of impulses and at other times initiating said regeneration responsive to the receipt of a different number of trains of impulses depending upon the digital values of one or more of the trains of impulses received by said separate means.

8. In a system as claimed in claim 6, means controlled by said separate means for at times, in dependence upon the digital value of on 01' the trains of impulses received thereby, originating an impulse and transmitting same to operate one of the automatic switches before said transmission of the unsuppressed regenerated trains of impulses.

9. In a system as claimed in claim 6, means normally operated to separate successive trains of said regenerated impulses by an interdigital pause of predetermined duration, and means controlling said last means to materially decrease the length of the pause between successive trains of said regenerated impulses if said regenerated trains are to be suppressed.

10. In a telephone or like system, automatic switches, means for seizing one of said switches and transmitting signals thereto corresponding to the digits of a called station number, common control equipment, means for associating said equipment with a switch when seized, means 10 in said equipment for registering the signals for each received digit, separate means in the equipment also operated responsive to the received signals and eiiective in accordance therewith to at times suppress certain of the signals registered by said registering means, and means controlled by said registering means to retransmit only the registered signals not suppressed by said last means. v

REGINAID TAYLOR. GEORGE THOMAS BAKER. 

